Cationic lipid reagents are the most effective and simplest method for DNA transfection of eukaryotic cells. A number of such reagents are known to the art, e.g. as described in U.S. patent applications 08/090,290, abandoned, 08/195,866, 08/171,232. Lipofectin.TM. (Gibco/BRL:Life Technologies, Inc., Gaithersburg, Md.; Felgner, P. L., et al. (1987) Proc. Natl. Acad. Sci. USA 84:7413) and LipofectACE.TM. (Whitt, M. A., et al. (1991) Focus 13:8) reagents contain monocationic lipids and are highly effective at transfection in the presence or absence of serum (Brunette, E., et al. (1992) Nuc. Acids Res. 20:1151; Ciccarone, V., et al. (1993) Focus 15, 80.). LipofectAMINE.TM. reagent (U.S. Pat. No. 5,334,761; Gibco/BRL:Life Technologies, Inc., Gaithersburg, Md.) contains a polycationic lipid and is up to 30-fold more active in serum-free transfection than the monocationic reagents (Hawley-Nelson, P., et al. (1993) Focus 15:73). However LipofectAMINE.TM. transfection activity is decreased in the presence of serum and is roughly equal to that of the monocationic reagents.
U.S. Pat. No. 5,286,634 of Stadler et al. for "Synergistic Method for Host Cell Transformation" issued Feb. 15, 1994 discloses the use of a polycationic compound to treat a host cell for a period of time prior to treating with a DNA-liposome complex to improve transformation of the cell. The invention was exemplified using plant cells which do not require serum in culture media or in vivo. The method of said patent is not believed effective in enhancing transfection of mammalian cells because the preferred polycationic compound of said patent (Polybrene.TM.), is toxic to mammalian cells in the absence of serum.
A problem with transfection of eukaryotic cells by means of liposomes is the fact that culturing such cells in vitro requires the use of serum in the medium for best results, and the use of serum in culture media is standard in the art. However, the use of serum in the culture medium substantially inhibits the efficiency of liposome transfection. Further, in the transfection of animal cells in vivo, serum is inherently present, again with an inhibiting effect on the efficiency of liposome transfection. Therefore a need exists for a method of eukaryotic transfection in the presence of serum which counteracts the inhibiting effects of the serum.
In addition, some liposomes are toxic to the cells being transformed. Thus, a method for counteracting the toxic effects of liposomes is needed to improve the efficiency of liposome transfection of eukaryotic cells.
All publications and patents referred to herein are specifically incorporated by reference in their entirety.